KR20120026506A - Treatment of polishing pad window - Google Patents

Abstract

A window of solid light-transmissive polymer is formed in the polishing pad, and one or more surfaces of the window are treated to increase the smoothness of the one or more surfaces.

Description

Processing method of polishing pad window {TREATMENT OF POLISHING PAD WINDOW}

This specification relates to the manufacture of polishing pads for use in chemical mechanical polishing (CMP).

In the process of manufacturing modern semiconductor integrated circuits (ICs), it is often necessary to planarize the outer surface of the substrate. Planarization, for example, is the top of the base layer, leaving a conductive material between the raised pattern of the insulating layer to form lines, plugs and via (s) that provide a conductive path between the thin film circuits on the substrate. It may be necessary to polish the conductive filler layer until the face is exposed. In addition, planarization may be necessary to planarize and thin the oxide layer to provide a suitable plane for photolithography.

One method for achieving semiconductor substrate planarization or topography removal is chemical mechanical polishing (CMP). Conventional chemical mechanical polishing (CMP) processes involve pressing the substrate against a rotating polishing pad in the presence of the polishing slurry.

In general, it is necessary to detect when the desired surface planarity or layer thickness has been reached, or when the base layer has been exposed to determine whether to stop polishing. Several techniques have been developed for in-situ detection of endpoints during the CMP process. For example, an optical monitoring system has been employed to measure in-situ the uniformity of a layer on a substrate while polishing the layer. The optical monitoring system can include a light source that directs the light beam towards the substrate during polishing, a detector that measures light reflected from the substrate, and a computer that analyzes the signal from the detector and calculates whether an endpoint has been detected. In some CMP systems, the light beam is directed towards the substrate through a window in the polishing pad.

In one aspect, a method of forming a window in a polishing pad includes forming a window of solid light-transmitting polymer in the polishing pad, and treating one or more surfaces of the window to increase smoothness of the one or more surfaces. It comprises the step of.

Embodiments may include one or more of the following. Treating one or more surfaces of the window may be performed after the window is formed in the polishing pad. Forming a window includes positioning a body of solid light-transmissive polymer in a mold, dispensing a liquid polishing pad precursor into the mold, curing the liquid precursor to be molded into a body of solid light-transmissive polymer ( forming a body comprising a solid abrasive material, and cutting a polishing pad having a portion of the solid abrasive material and a portion of the body of a solid light-transmissive polymer. Forming the window may include forming a top surface of the window closer to the polishing surface of the polishing layer and forming a bottom surface closer to the bottom surface of the polishing layer. The top face may be located in substantially the same plane as the polishing surface and the bottom face may be located in substantially the same plane as the bottom surface. Treating one or more surfaces of the window may include treating the top and / or bottom surfaces of the window. Treating one or more surfaces of the window may include heating one or more surfaces, for example, applying a heated body to one or more surfaces, optionally a heated body on one or more surfaces. Pressing may comprise, for example, ironing one or more surfaces. The body may be heated to a temperature of at least 150 ° C, for example between 150 ° C and 250 ° C, for example about 200 ° C. The solid light-transmissive polymer may be polyurethane. Heating the one or more surfaces may raise the temperature of the one or more surfaces above the glass transition temperature of the solid light-transmissive polymer. Treating one or more surfaces may comprise applying a solvent to one or more surfaces. The polishing pad may comprise a polishing layer formed of polyurethane with microsphere filler.

Potential advantages may include one or more of the following. The transmission of light passing through the window can be increased, resulting in reduced noise and increased reliability of endpoint detection. Pad-to-pad non-homogeneity in the window transmission side can be reduced. Other features and advantages will be apparent from the description, drawings, and claims.

1 is a schematic side cross-sectional view of a chemical mechanical polishing apparatus having an optical monitoring system for end point detection.
2 is a simplified schematic cross-sectional view of a polishing pad with a window.
3 is a simplified plan view of the polishing pad of FIG. 2.
4 is a simplified schematic cross-sectional view of a polishing pad with a pressure sensitive adhesive and a liner.
5 is a schematic perspective view of a block of solid light-transmissive material for use in making a polishing pad window.
6 is a schematic side cross-sectional view showing a liquid abrasive layer precursor in a mold with a block of solid light-transmissive material.
7 is a schematic perspective view of a body of cured abrasive material molded into a block of solid light-transmissive material.
8 is a schematic cross-sectional view of a polishing pad skived from a body of cured abrasive material.
9 is a schematic cross-sectional view of the polishing pad window to be heat treated.

One potential problem in manufacturing a polishing pad is the roughness of the pad window surface. For example, skiving processes can leave serrations, scratches or other roughness on the window. Such roughness can cause scattering, reducing the transmission of the window and increasing noise in the optical monitoring system. However, by treating the window, for example with heat, the window surface can be smoothed. Smoother windows have greater transmission, thus reducing noise in optical monitoring systems and improving the reliability of endpoint detection. In addition, pad to pad non-homogeneity in terms of window transmittance can be reduced.

 As shown in FIG. 1, the CMP apparatus 10 includes a polishing head 12 for holding the semiconductor substrate 14 against the polishing pad 18 on the platen 16.

Substrates can be, for example, product substrates (such as including multiple memory or processor dies), test substrates, bare substrates, and gating substrates. The substrate may be at other stages of integrated circuit fabrication, for example, the substrate may be a bare waiter, or may include one or more deposited and / or patterned layers. The term "substrate" may include circular disks and rectangular sheets.

As the platen rotates about its central axis, the polishing head 12 applies pressure to the substrate 14 against the polishing pad 18. In addition, the polishing head 12 is usually rotated about the central axis of the polishing head and translated across the surface of the platen 16 using a drive shaft or translation arm 32. An abrasive liquid 30, for example an abrasive slurry, may be dispensed onto the polishing pad. Under the action of the polishing liquid, the pressure and relative movement between the substrate and the polishing surface causes polishing of the substrate. A conditioner may abrasion the surface of the polishing pad 18 to maintain the roughness of the polishing pad.

The optical monitoring system includes a detector 38, such as a photo spectrophotometer, and a light source 36, such as a white light source, in optical communication with the window 40 in the polishing pad 18. The light source and detector may be located within platen 16 and rotate with platen 16 such that the monitoring light beam sweeps across the substrate once per rotation of the platen. For example, two bifurcated optical fibers 34 carry light from the light source 36 through the platen 18 and are directed through the window 40 to the substrate 14 and the substrate 14. Light reflected from) may pass back through the optical fiber 34 to the detector 38. Alternatively, the light source and detector may be a stationary component located under the platen, and the optical aperture may extend through the platen under window 40 to intermittently pass a monitoring light beam through the substrate. Although a broad spectrum, for example white light, may also be used, the light source may employ any wavelength from approximately far infrared to ultraviolet, such as red light.

Referring to FIG. 2, the polishing pad 18 may include a polishing layer 20 having a polishing surface 24 in contact with the substrate and a backing layer 22 adhesively fixed to the platen 16. . The abrasive layer 20 may be of a material suitable for bulk planarization of the exposed layer on the substrate. Such an abrasive layer may be formed of a polyurethane material, for example with a filler such as hollow microspheres, for example the abrasive layer may be an IC-1000 material available from Rohm & Hass. The back layer 22 may be more compressive than the abrasive layer 20. In some embodiments, the polishing pad comprises only a polishing layer, and / or the polishing layer is a relatively soft material suitable for the buffing process, such as a porous coating with a large amount of vertically oriented pores. to be. In some embodiments, grooves may be formed in the polishing pad 24.

Window 40 may be a transparent material, such as a solid light-transmissive material, for example, relatively pure polyurethane, without filler. The window 40 may be bonded to the abrasive layer 20 without adhesive, for example, the abrasive layer 20 and adjacent edges of the window 40 may be molded together. The top surface of the window 40 may be located in the same plane as the polishing surface 24, and the bottom surface of the window 40 may be located in the same plane as the bottom of the polishing layer 20. The abrasive layer 18 may completely surround the window 40. The opening in the back layer 22 is aligned with the window 40 in the polishing layer 20.

Referring to FIG. 3, in one embodiment, the polishing pad 18 has a radius R of 15.0 inches (381.00 mm) and a corresponding diameter of 30 inches. In other embodiments, the polishing pad 18 may have a radius of 15.25 inches (387.35 mm) or 15.5 inches (393.70 mm) and a corresponding diameter of 30.5 inches or 31 inches. The optical monitoring system can use an area having a width of about 0.5 inch (12.70 mm) and a length of 0.75 inch (19.05 mm), wherein the distance D between the center of the area and the center of the polishing pad 18 is 7.5 inches. (190.50 mm). Thus, the window should cover at least the above areas. For example, the window may have a length of about 2.25 inches (57.15 mm) and a width of about 0.75 inches (19.05 mm). Both the polishing pad and the window can have a thickness of about 0.02 to 0.20 inch, for example 0.05 to 0.08 inch (1.27 to 2.03 mm). The window 40 may have a rectangular shape with longer dimensions of the sides substantially parallel to the radius of the polishing pad passing through the center of the window. However, the window 40 can have other shapes, such as circular or elliptical, and the center of the window need not be located in the center of the area used by the optical monitoring system.

Referring to FIG. 4, prior to installation on the platen, the polishing pad 18 may also include a liner 72 and a pressure sensitive adhesive 70 that spans the bottom surface 23 of the polishing pad. Can be. In use, the liner 72 is peeled from the polishing layer 20, and the polishing pad 18 is applied to the platen by the pressure-sensitive adhesive 70. The pressure sensitive adhesive 70 and liner 72 may reach the window 40, or either or both may be in the area of the window 40 and just around the area of the window 40. Can be removed.

5-9, the method of constructing the polishing pad will now be discussed. Initially, a block 100 of solid light transmissive polymer material is formed. For example, blocks of solid polyurethane without fillers that inhibit permeation can be cast and cut to the desired dimensions. Such a block may have a cross-sectional dimension in the same xy plane as the window to be formed in the polishing pad, but a much thicker dimension in the z plane, for example at least ten times thicker, such as about 20-50 times thicker. Can have For example, the window block may have a length L and a thickness T of 2.25 inches (57.15 mm) and a width W of about 0.75 inches (19.05 mm). The sides may be roughened 102, 104, for example, to improve adhesion to the polymeric layer material during molding.

Referring to FIG. 6, a block 100 may be located in a mold 140 that is subsequently filled with the liquid precursor 150 of the polishing layer. The mold 140 may be filled approximately the same height as the block 100, for example, the block 100 may be locked or protrude slightly above the liquid 150.

Referring to FIG. 7, the liquid precursor is then cured, for example baked and removed from the mold 150. For example, the liquid polyurethane can be cured to form a solid plastic body 160 molded into the block 100. The plastic body 160 is within the xy plane, for example 10 inches (254 mm), 15.0 inches (381.00 mm), 15.25 inches (387.35 mm), 15.5 inches (393.70 mm), 21 inches (533.40 mm) or 21.25 A circular disk with a radius of an inch (539.75 mm), which may be larger than the final polishing pad or have substantially the same lateral dimension, but along the z axis a much thicker dimension than the final polishing pad, e.g. For example at least 10 times thicker.

Referring to FIG. 8, the thin abrasive layer 20 is then cut from the body 160, for example by skiving in the x-y plane, for example by the blade 170. Since the skiving cuts through the block 100, the skyed portion of the block 100 forms a window 40 molded into the abrasive layer 20. The skiving process produces small-scale (eg, 5 to 200 microns deep) surface irregularities, such as scratching, serrations, or other roughness, on both the top and bottom surfaces 42 and 40 of the window 40. I can leave it. For the top surface, the presence of water or slurry during polishing may provide index-matching to the pad material, which is the tendency of surface irregularities to cause scattering as the light beam passes through the window top surface. Can be reduced. However, if the bottom face of the window is in contact with air, as discussed above, surface unevenness causes scattering as the light beam passes through the window bottom face, reducing the transmission of the window and increasing noise in the optical monitoring system. You can.

After the window is skived, the top and / or bottom surfaces of the window 40 may be treated to reduce surface unevenness and increase surface smoothness, thereby reducing the tendency to scatter light on the window surface. Can be.

As an example, the surface of the window may be heated to soften the window slightly, thereby allowing the surface to be fluid or pressed flat. For example, the window material is sufficiently elevated to allow the window to remain solid but more easily deform and reach a smooth surface situation, for example, it is sufficiently elevated to allow the window material to deform without fracture plastic. For example, the window material can be elevated to or above its glass transition temperature. In addition, if the window material is already in the glassy phase at room temperature, the application of heat may further soften the window material. However, the temperature need not be raised above the melting point of the window material. There may be deformation in response to gravity where the pad material flows and self-leveling, or in response to pressure from a rigid solid portion. For example, in order to press out the surface unevenness and leave the window surface more remarkably smooth than after the skiving process, the manufacturer has already removed the solidified window material (but optionally the rest of the polishing pad 20). May be excluded), and may be pressurized to a portion of the heated rigidity. The heated portion can be moved laterally across the window so that the surface unevenness can be smoothed, for example, the window can effectively be ironed flat.

In general, in order to depress surface unevenness, high pressure must be applied to the rigid part at low temperatures. On the other hand, the temperature should not be too high so that the window material does not melt or burn.

In some embodiments, for example for a urethane-based window, the surface of the heated portion to be in contact with the window is at a temperature of at least 150 ° C, for example at a temperature of 150 ° C to 250 ° C, for example about 200 ° C. It can be raised to the temperature of.

In some embodiments, the window material may be polished with heat treatment.

Referring to FIG. 9, the heating system 180 includes a rigid thermally conductive body 182 having a smooth surface 184, such as a metal plate, applied to a surface, such as the bottom surface 44 of the window 40. It may include. For example, body 182 may be heated by resistive heating component 186 connected to power supply 188. The resistive heating element 186 may be embedded in the thermally conductive body 182, or in a separate portion attached to the thermally conductive body 182, as shown. For example, the heating system may be a consumer ironing device or may be a soldering iron with a tip on which a thermally conductive plate is assembled.

If the polishing pad 18 comprises a backing layer 22, the polishing layer 20 with the molded window 40 before or after the treatment of the window 40, for example by means of a pressure-sensitive adhesive, ) May be fixed to the back layer 22.

As another example of surface treatment, chemical solvents may be applied to the top and / or bottom window surfaces to dissolve scratches or surface irregularities. Urethane solvents are commercially available.

Many embodiments have been disclosed. Nevertheless, it should be understood that various modifications may be made within the spirit and purpose of the present disclosure. For example, while context has been described above with respect to a window molded into the abrasive layer, the window may be skyed from the block and secured in a hole in the abrasive layer, for example by an adhesive. In this case, the window can be processed before or after installation in the polishing pad. In addition, processes other than skiving, such as molding, may cause surface irregularities on the window surface. Accordingly, other embodiments are to be understood as being within the scope of the following claims.

Claims (15)

A method of forming a window in a polishing pad,
Forming a window of solid light-transmissive polymer in the polishing pad; And
Treating one or more surfaces of the window to increase the smoothness of the one or more surfaces of the window
Including,
A method of forming a window in a polishing pad.
The method of claim 1,
Treating one or more surfaces of the window is performed after the window is formed in the polishing pad,
A method of forming a window in a polishing pad.
The method of claim 1,
Forming the window,
Positioning a body of solid light-transmissive polymer in the mold,
Dispensing a liquid polishing pad precursor into the mold,
Curing the liquid precursor to form a body comprising a solid abrasive material molded into the body of the solid light-transmissive polymer, and
Cutting a polishing pad comprising a portion of the solid abrasive material and a portion of the body of the solid light-transmissive polymer
Including,
A method of forming a window in a polishing pad.
The method of claim 1,
Forming the window comprises forming a top surface of the window closer to the polishing surface of the polishing layer and forming a bottom surface closer to the bottom surface of the polishing layer,
A method of forming a window in a polishing pad.
The method of claim 4, wherein
The top surface is located in substantially the same plane as the polishing surface, and the bottom face is located in substantially the same plane as the bottom face,
A method of forming a window in a polishing pad.
The method of claim 4, wherein
Treating one or more surfaces of the window includes treating the top surface of the window,
A method of forming a window in a polishing pad.
The method of claim 4, wherein
Treating one or more surfaces of the window comprises treating the bottom face of the window,
A method of forming a window in a polishing pad.
The method of claim 1,
Treating one or more surfaces of the window includes heating the one or more surfaces,
A method of forming a window in a polishing pad.
The method of claim 8,
Heating the one or more surfaces includes ironing the one or more surfaces,
A method of forming a window in a polishing pad.
The method of claim 8,
Heating the one or more surfaces comprises applying a heated body to the one or more surfaces,
A method of forming a window in a polishing pad.
The method of claim 10,
The heated body is heated to a temperature of 150 ° C. or greater than 150 ° C.,
A method of forming a window in a polishing pad.
The method of claim 11,
The temperature is 150 ℃ to 250 ℃,
A method of forming a window in a polishing pad.
The method of claim 11,
Wherein said solid light-transmissive polymer comprises polyurethane;
A method of forming a window in a polishing pad.
The method of claim 8,
By heating the at least one surface, the temperature of the at least one surface is raised above the glass transition temperature of the solid light-transmissive polymer,
A method of forming a window in a polishing pad.
The method of claim 1,
Wherein the polishing pad comprises a polishing layer formed of polyurethane with microsphere fillers,
A method of forming a window in a polishing pad.

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